Various pulverizers are widely used, for example, a media agitating pulverizer such as a conventional ball mill or an improved type of pulverizer which has working parts associated with the pulverizer such as agitator pins or discs that move pulverizing media, such as balls, beads and pellets, and pulverizes a material utilizing impact, friction and compression forces produced by the kinetic energy of the media, a roller mill that pulverizes a material utilizing compression force produced by a roller, a jet mill that pulverizes a material utilizing impact force produced by forcing the material to strike the internal lining at a high speed, a hammer mill or a pin mill or a disc mill that pulverizes a material utilizing impact produced by rotation of a rotor to which a pulverizing medium, for examples, a hammer, a blade or a pin is fixed or a colloid mill that utilizes shearing force.
In particular, a wet media agitating type pulverizer achieves a high pulverizing efficiency and is highly suitable for fine pulverization at a sub-micron level. In this type conventional pulverizer, the aforementioned members, such as a slit bar, an agitating pin, an agitating disc, a sleeve or a collar, are formed from metals and, more specifically, formed mainly from ordinary structure-purposed rolled steel materials specified by JIS G4305, 3101 including SUS304. The screen, having wedge wire type slits, is integrally formed by joining each slit bar individually to a base by brazing. For an improved abrasion resistance, the hardness of the surfaces of the slit bars is increased by induction quenching, thermal spraying of stellite, or other measures. It is well known that pulverizer members formed from materials other than the aforementioned metals, including natural stones such as agate, ceramics such as alumina ceramic or zirconia ceramic, resins and hard metals have also been used in recent years.
However, the members formed from materials as mentioned above have problems in that they easily abrade and large amounts of abrasional debris contaminate the material to be pulverized, thereby degrading the properties and qualities of the pulverized material and various materials produced from the pulverized material. The problem of contamination with abrasional debris becomes serious particularly if the pulverized material is used for so-called high tech materials such as fine ceramic materials, magnetic materials ad electronics materials.
To solve the problems, JP-A-04-285063 proposes a member for use in a pulverizer formed from a material having well-balanced properties needed for a material of members of a pulverizer, in particular, abrasion resistance, strength and toughness. More specifically, the member is formed from a ceramic containing Al.sub.2 O.sub.3 as a main component, ZrO.sub.2 within a range of 20-40 wt. % with at least 50 vol. % of the crystal structure being tetragonal, TiO.sub.2 within a range of 1-5 wt. %, and MgO within a range of 0.1-1 wt. %, wherein the average crystal grain diameter of Al.sub.2 O.sub.3 is within a range of 1.5-5 .mu.m and wherein at least 80% of the Zr.sub.2 O is present in the grain boundary of Al.sub.2 O.sub.3. However, this member is not sufficient in the hardness, strength and toughness that are needed for a member of a pulverizer, causing problems with abrasion resistance and impact resistance in practical use.